Snap button fastener



FIG. 1 is a side view of a snap button fastener showing my new design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a front view thereof; and,

FIG. 5 is a back view. 

The ornamental design for a snap button fastener, as shown and described. 